Clamping mandrels usable for the rotatable support of paper rolls, such as are used in connection with web-fed rotary printing presses, are known from U.S. Pat. No. 4,149,682, U.S. Pat. No. 4,951,894 and U.S. Pat. No. 4,715,553. Ejecting devices are provided on the clamping mandrels, by use of which the tube on which the paper web is wound can be stripped off the clamping mandrels. Spring elements, that are provided on the ejecting device, are elastically prestressed in the course of inserting the clamping mandrel into the tube. When the clamping mandrel is pulled back out of the tube for changing the paper web, the prestress of the spring elements assures that the tube is stripped off the two oppositely located clamping mandrels.
The disadvantage of this type of structure of an ejecting device lies in that the force, by which the tube can be stripped off the clamping mandrel, is limited by the type of construction of the spring elements. It is moreover necessary to overcome the prestress of the spring elements in the course of inserting the clamping mandrels into the tube.
A clamping mandrel is known from DE 28 14 338 A1, in which a displaceable ring, which can rotate together with the mandrel, is arranged between the detent flange of the mandrel and the tube. An actuating device, which is fixed in place on a frame, is provided for ejecting the tube. Claws are provided on the actuating device, wherein the ring can freely rotate in one position of the claws, namely the position of rest, and is not in engagement with the claws. In the course of operating the actuating device the claws are pressed against the ring, so that the tube can be stripped off the clamping mandrel.
It is disadvantageous in connection with the actuating device known from DE 28 14 338 A1 that, because of its mechanical drive mechanism, the ejecting device requires a large structural volume.
U.S. Pat. No. 2,949,313 discloses an adjusting element which is rotatably seated around its center axis and which can be axially actuated. The adjusting element can be displaced between a position of rest and at least one working position by use of an axially displaceable, fluid-driven piston.